Komatsu GD661A-1(S/N 10001-UP)

The Komatsu GD661A-1 (S/N 10001-up) is a large-class motor grader from Komatsu's A-1 generation grader lineup, built around the naturally aspirated, mechanically injected Komatsu S6D105 (6D105-1 series) six-cylinder diesel rated 179.7 hp (134 kW) at 2500 rpm with 6.49 L (396.1 cu in) displacement. Operating weight in standard configuration is about 13,300 kg (29,322 lb); actual weight varies by tire size, attachments, and cab/ROPS options. Drive runs through a torque-converter and power-shift transmission with a lock-up clutch to four tandem-mounted rear wheels, carrying a 3.72 m (12.2 ft) moldboard on a 2.6 m (8.5 ft) blade base. It shares its chassis family and service-manual coverage with the smaller GD611A-1 and related GD613A-1, GD615A-1, GD621A-1, GD622A-1, and GD623A-1 models, plus the larger GD663A-1 and GD672A-1, all part of the same pre-electronic Komatsu grader generation. Exact production years for this specific serial block are not documented in available sources; the plain numeric S/N 10001-up range places it in Komatsu's era before PIN-based serial identification. Configurations offered included the standard grading blade, an optional scarifier or ripper, and different tire fitments including 13.00-24-10PR.

Across the A-1 family, Komatsu scaled the same torque-converter/power-shift architecture and naturally aspirated S6D105-family engine across several blade-class variants, differing mainly in horsepower rating, moldboard length, and wheelbase rather than in drivetrain technology. Later Komatsu grader generations moved to turbocharged, electronically controlled engines with onboard diagnostics; the GD661A-1 predates that shift, so there is no ECM and no digital fault-code readout - the operator relies on the central warning lamp/buzzer and individual monitor lamps checked against the service manual's troubleshooting tables. That mechanical simplicity is why these units still circulate in the used and parts market: fewer sensors, no engine electronics to fail, straightforward mechanical fuel injection, and a drivetrain a competent grader mechanic can diagnose and rebuild without a factory scan tool. Parts commonality across the shared GD611A-1/GD661A-1/GD663A-1/GD672A-1 manual family also broadens the pool of interchangeable driveline, circle, and tandem-case components available in today's parts market.

Below: full specifications, fluids & capacities, the factory service schedule, common service parts, verified fault codes, what owners discuss, attachment guidance, the complete assembly directory, and a serial-number reference. Complete parts lists with full OEM part numbers, exploded diagrams, quantities, and fitment data are available free in Heavy Parts AI.